The present invention is directed to a device for feeding sheets or blanks into a processing machine, which is designed for converting the sheet or blank into a product, for example, a folding and gluing machine.
A feeding device is already known, which has a front stop and a conveying arrangement for feeding the bottom sheet of a pile underneath the front stop into a folder gluer, which operation is to be determined by a controllable rhythm. Such a device is described in detail in U.S. Pat. No. 3,907,278, whose disclosure is incorporated by reference thereto. In the patent, the sheet infeed arrangement consists of a transmission pulley provided with a unidirectional coupling which enables the driving of the conveyor belts in one direction only. The necessary drive occurs from a control shaft actuated intermittently by a connecting rod-and-crankshaft arrangement.
The device of the patent, however, has a serious drawback in that the stroke required by the sheet to be fed cannot be adapted to the particular length of the sheet. Thus, the device results in an inadequate shift for the infeed control.
In fact, if such a device is used, the sheet is moved forward through a distance corresponding to the conveyor belt movement caused by the connecting rod and crankshaft arrangement until the sheet will be nipped by the drive rollers which are actually in charge of terminating the infeed movement. The sheet infeed action is, thus, carried out in two consecutive steps by two interacting appliances, which can jeopardize a reliable control of the advance for the sheet during the step of being fed into the processing machine.